Combinatorial and High-Throughput Screening of Materials ...

ACS Combinatorial Science
REVIEW
Figure 42. Combinatorial screening of sensing film compositions using passive RFID sensors. (a) Phthalate plasticizers dimethyl phthalate N1, butyl
benzyl phthalate N2, di-(2-ethylhexyl) phthalate N3, dicapryl phthalate N4, and diisotridecyl phthalate N5. (b) Photo of an array of 48 RFID sensors
prepared for temperature-gradient evaluations of response of Nafion/phthalate compositions. (c) Results of principal components analysis of ΔF 1 , ΔF 2 ,
ΔF p , and ΔZ p responses of RFID sensors with six types of sensing films to H 2 O and ACN vapors upon annealing at 110 °C. Arrows illustrate the
H 2 O ACN Euclidean distances and the response direction of sensing films N0 N5 starting with ACN and ending with H 2 O response. 414
efforts to develop data mining techniques 97,98 and a database
system. 413 The developed data mining tools based on hierarchical
clustering maps (see Figure 41) have been applied to identify
several promising materials candidates such as In 99.5 Co 0.5 O x ,
W 99 Co 0.5 Y 0.5 O x , W 98.3 Ta 0.2 Y 1 Mg 0.5 O x , W 99.5 Ta 0.5 O x , and
W 99.5 Rh 0.5 O x with different gas-selectivity patterns. 100
Sensing materials have been also arranged into discrete arrays
and evaluated for their temperature stability using resonance
impedance measurements 414 based on passive radio frequency
415 417
identification (RFID) sensors with multivariable response.
These sensing materials were Nafion polymeric materials formulated
with five phthalate plasticizers as shown in Figure 42A.
Sensing film formulations and control sensing films without
plasticizers were deposited onto RFID sensors to form a 6 8
sensor array (Figure 42B), which was exposed to eight temperatures
ranging from 40 to 140 oC using a gradient temperature
heater, and their response stability and gas-selectivity response
patterns were evaluated upon exposure to water and acetonitrile
vapors. The multivariable responses of these sensors were further
examined using PCA (see Figure 42C). Nafion sensing films
formulated with dimethyl phthalate showed the largest improvement
in response diversity to these two vapors as indicated by the
largest Euclidean distance. This RFID-based sensing approach
demonstrated rapid, cost-effective, combinatorial screening of
sensing materials and preparation conditions.
The effects of variable 2-D composition of materials arrays
were investigated in sensors based on the change in the work
function of the catalytic metal gate (Pd, Pt, Rh, Ir) because of
chemical reactions on the metal surface. 418,419 These sensors are
attractive for detection of different gases (e.g., hydrogen sulphide,
ethylene, ethanol, different amines, and others). The
chemical reaction mechanisms in these sensors depend on the
specific gas molecules. Optimization approaches of materials for
these sensors involve several degrees of freedom. 420 To simplify
screening of the desired material compositions and to reduce a
common problem of batch-to-batch differences of hundreds of
individually made sensors for materials development, the scanning
light pulse technique (SLPT) has been developed. 421 423 In
SLPT, a focused light beam is scanned over a large area
semitransparent catalytic metal insulator semiconductor
structure and the photocurrent generated in the semiconductor
depletion region is measured to create a 2-D response pattern of
the sensing film (aka “a chemical image”).
These chemical images were used to optimize properties such as
chemical sensitivity, selectivity, and stability. 343 When combined
with surface-characterization methods, this information also has led
to the increased knowledge of gas response phenomena. It was
suggested that a 2-D gradient made from two types of metal films as
a double layer structure should provide new capabilities for sensor
materials optimization, unavailable from thickness gradients of
single metal films. 424 To make a 2-D gradient, the first metal film
was evaporated on the insulator with the linear thickness variation
in one dimension by moving a shutter with a constant speed in
front of the substrate during evaporation. On top of the first
gradient thickness film, a second metal film was evaporated with a
linear thickness variation perpendicular to the first film. As the
validation of the 2-D array deposition, the response of devices with
1-D thickness gradients of Pd, Pt, and Ir films to several gases has
been studied with SLPT demonstrating results similar to those of
corresponding discrete components. 343
The 2-D gradients have been used for studies and optimization
of the two-metal structures 343,424 and for determination of the
effects of the insulator surface properties on the magnitude of
sensing response. 425 2-D gradients of Pd/Rh film compositions
were also studied to identify materials compositions for the most
stable performance. 343 The Pd/Rh film compositions were tested
for their response stability to 1000 ppm of hydrogen upon aging
for 24 h at 400 °C while exposed to 250 ppm of hydrogen (see
Figure 43A, B). This accelerated aging experiment of the 2-D
gradient film surface demonstrated the existence of two most
stable local regions. One region was a “valley” of a stable response
shown as a dark color in Figure 43C. Another region was a thicker
part of the two-component film with a ∼20-nm thick Rh film and
a ∼23-nm thick Pd film. This new knowledge inspired new
questions of position stability of the “valley” and the possibility to
improve sensor stability by an initial annealing process.
3.5. Biomaterials. Biomaterials are defined as any substance
(other than a drug) or combination of substances, synthetic or
natural in origin, which can be used for any period of time, as a
whole or as a part of a system which treats, augments, or replaces
any tissue, organ, or function of the body. 426 Biomaterials can be
biopolymers, ceramics, and composites of organic/organometallic/inorganic
materials that can be used for in vivo/in vitro
applications. 426 428 Examples of biomaterials uses are implants,
organs or parts of them, materials designed and used for drug
delivery, heart valves, bone cement, artificial ligaments/tendons,
blood vessel prosthesis, contact lenses, skin repair devices, and
dental implants. 428 Most of recent research on biomaterials is in
the areas of reparative medicine and delivery of biologically active
substances (e.g., drugs or gene) for therapeutic applications. 429
617 dx.doi.org/10.1021/co200007w |ACS Comb. Sci. 2011, 13, 579–633